Playing this video requires the latest flash player from Adobe.
Download link (right click and 'save-as') for playing in VLC or other compatible player.
It is generally believed that modification of general relativity inevitably introduce extra physical degree(s) of freedom.
In this talk I argue that this is not the case by constructing modified gravity theories with two local physical degrees of freedom. After classifying such theories into two types, I show explicit examples and discuss their cosmology and phenomenology.